The present invention relates to photosensitive compositions or more particularly to a class of unique diazonium compounds suitable for use in the lithographic arts for the production of printing plates and other photographic elements such as photoresists and color proofing films.
It is known that diazonium compounds characteristically vary widely in their light sensitivity, or speed, and their aging ability or shelf life. It is generally acknowledged that light speed and shelf life bear a reciprocal relationship to one another. That is, as light sensitivity increases, shelf life decreases and vice versa. Those skilled in the art are constantly seeking new ways of simultaneously increasing both properties. As a rule of thumb, commercial requirements demand that a lithographic printing plate have a shelf life of at least twelve months and preferably at least eighteen months prior to significant light speed degradation.
One method of achieving improved shelf life is to render a compound, considered to possess high light sensitivity, solvent soluble, from an otherwise water-soluble form. This approach will reduce the compound's hygroscopic nature which can and will adversely affect aging. However, this process will not improve the compound's light speed.
Using a technique described in U.S. patent application Ser. No. 359,458, filed on Mar. 18, 1982, now U.S. Pat. No. 4,414,311 and which is incorporated herein by reference, certain benefits are realized when the diazo to be applied to a metallic plate surface is coated via a cathodic electrodeposition from an electrolyte. Using such a technique results in a coating having marked improvement of adhesion and overall lithographic performance. It is observed that some diazonium compounds have enhanced stability properties when an electrical potential is applied as opposed to standard coating application methods. Generally, those diazos having the greatest stability when exposed to such an electrical force that would be used to create a cathodically deposited surface tend to have rather low UV sensitivity. In order to provide a compound capable of withstanding electrical potential, while still retaining high light speed, new approaches are taken to synthesize novel diazo-based polymers.